The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to resect, coagulate, ablate and aspirate cartilage, bone and tissue, such as sinus tissue, or meniscus and synovial tissue in a joint.
Conventional electrosurgical methods are widely used since they generally reduce patient bleeding associated with tissue cutting operations and improve the surgeon""s visibility. These electrosurgical devices and procedures, however, suffer from a number of disadvantages. For example, monopolar electrosurgery methods generally direct electric current along a defined path from the exposed or active electrode through the patient""s body to the return electrode, which is externally attached to a suitable location on the patient""s skin. In addition, since the defined path through the patient""s body has a relatively high electrical impedance, large voltage differences must typically be applied between the active and return electrodes to generate a current suitable for cutling or coagulation of the target tissue. This current, however, may inadvertently flow along localized pathways in the body having less impedance than the defined electrical path. This situation will substantially increase the current flowing through these paths, possibly causing damage to or destroying tissue along and surrounding this pathway.
Bipolar electrosurgical devices have an inherent advantage over monopolar devices because the return current path does not flow through the patient beyond the immediate site of application of the bipolar electrodes. In bipolar devices, both the active and return electrode are typically exposed so that they may both contact tissue, thereby providing a return current path from the active to the return electrode through the tissue. One drawback with this configuration, however, is that the return electrode may cause tissue desiccation or destruction at its contact point with the patient""s tissue.
Another limitation of conventional bipolar and monopolar electrosurgery devices is that they are not suitable for the precise removal (i.e., ablation) or tissue. In addition, conventional electrosurgical methods are generally not that effective with certain types of tissue, and in certain types of environments within the body. For example, loose or elastic connective tissue, such as the synovial tissue in joints, is extremely difficult (if not impossible) to remove with conventional electrosurgical instruments because the flexible tissue tends to move away from the instrument when it is brought against this tissue. Since conventional techniques rely mainly on conducting current through the tissue, they are not effective when the instrument cannot be brought adjacent to or in contact with the elastic tissue for a long enough period of time to energize the electrode and conduct current through the tissue.
The use of electrosurgical procedures (both monopolar and bipolar) in electrically conductive environments can be further problematic. For example, many arthroscopic procedures require flushing of the region to be treated with isotonic saline, both to maintain an isotonic environment and to keep the field of view clear. However, the presence of saline, which is a highly conductive electrolyte, can cause shorting of the active electrode(s) in conventional monopolar and bipolar electrosurgery. Such shorting causes unnecessary heating in the treatment environment and can further cause non-specific tissue destruction.
Conventional electrosurgical cutting or resecting devices also tend to leave the operating field cluttered with tissue fragments that have been removed or resected from the target tissue. These tissue fragments make visualization of the surgical site extremely difficult. Removing these tissue fragments can also be problematic. Similar to synovial tissue, it is difficult to maintain contact with tissue fragments long enough to ablate the tissue fragments in situ with conventional devices. To solve this problem, the surgical site is periodically or continuously aspirated during the procedure. However, the tissue fragments often clog the aspiration lumen of the suction instrument, forcing the surgeon to remove the instrument to clear the aspiration lumen or to introduce another suction instrument, which increases the length and complexity of the procedure.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within or on the surface of a patient""s body. In particular, methods and apparatus are provided for resecting, cutting, partially ablating, aspirating or otherwise removing tissue from a target site, and ablating the tissue in situ. The systems and methods of the present invention are particularly useful for ablation and hemostasis of tissue in sinus surgery (e.g., chronic sinusitis and/or removal of polypectomies) and for resecting and ablating soft tissue structures, such as the meniscus and synovial tissue within a joint.
In one aspect of the invention, a method comprises introducing a distal end of an electrosurgical instrument, such as a probe or a catheter, to the target site, and aspirating tissue from the target site through one or more aspiration lumen(s) in the instrument. High frequency voltage is applied between one or more aspiration electrode(s) coupled to the aspiration lumen(s) and one or more return electrode(s) so that an electric current flows therebetween. The high frequency voltage is sufficient to remove or ablate at least a portion of the tissue before the tissue passes into the aspiration lumen(s). This partial or total ablation reduces the size of the aspirated tissue fragments to inhibit clogging of the aspiration lumen.
The aspiration electrode(s) are usually located near or at the distal opening of the aspiration lumen so that tissue can be partially ablated before it becomes clogged in the aspiration lumen. In some embodiments, the aspiration electrodes(s) are adjacent to the distal opening, or they may extend across the distal opening of the lumen. The latter configuration has the advantage of ensuring that the tissue passing through the aspiration lumen will contact the aspiration electrode(s). In other embodiments, the aspiration electrode(s) may be positioned within the aspiration lumen just proximal of the distal opening. The aspiration electrode(s) may comprise a loop, a coiled structure, a hook, or any other geometry suitable for ablating the aspirated tissue. In an exemplary embodiment, the electrosurgical probe comprises a pair of loop electrodes disposed across the distal end of the suction lumen.
The electrosurgical probe will preferably also include one or more ablation electrode(s) for removing or ablating tissue at the target site. Typically, the ablation electrode(s) are different from the aspiration electrode(s), although the same electrodes may serve both functions. In an exemplary embodiment, the probe includes a plurality of electrically isolated electrode terminals surrounding the distal opening of the aspiration lumen. High frequency voltage is applied between the electrode terminals and a return electrode to ablate tissue at the target site. During the procedure, fluid and/or non-ablated tissue fragments are aspirated from the target site to improve visualization. Preferably, one or more of the electrode terminals are loop electrodes that extend across the distal opening of the suction lumen to ablate, or at least reduce the volume of, the tissue fragments, thereby inhibiting clogging of the lumen. The aspiration or loop electrodes may be energized with the active electrode terminal(s), or they may be isolated from the electrode terminal(s) so that the surgeon may select which electrodes are activated during the procedure.
In some embodiments, the return electrode(s) comprises an annular electrode member on the probe itself, spaced proximally from the aspiration and ablation electrodes. In these embodiments, electrically conducting fluid, such as isotonic saline, is preferably used to generate a current flow path between the aspiration electrode(s) and the return electrode(s). High frequency voltage is then applied between the electrode terminal(s) and the return electrode(s) through the current flow path created by the electrically conducting fluid. Depending on the procedure, the electrically conductive fluid may be delivered to the target site through, for example, a fluid lumen in the probe or a separate instrument, or the fluid may already be present at the target site, as is the case in many arthroscopic procedures.
In a specific configuration, the tissue is remove molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the electrode terminal(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel or saline) between the electrode terminal(s) and the tissue. Within the vaporized fluid, a ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference.
The present invention offers a number of advantages over conventional electrosurgery, microdebrider and laser techniques for removing soft tissue in arthroscopic, sinus or other surgical procedures. The ability to precisely control the volumetric removal of tissue results in a field of tissue ablation or removal that is very defined, consistent and predictable. The shallow depth of tissue heating also helps to minimize or completely eliminate damage to healthy tissue structures, cartilage, bone and/or cranial nerves that are often adjacent the target sinus tissue. In addition, small blood vessels at the target site are simultaneously cauterized and sealed as the tissue is removed to continuously maintain hemostasis during the procedure. This increases the surgeon""s field of view, and shortens the length of the procedure. Moreover, since the present invention allows for the use of electrically conductive fluid (contrary to prior art bipolar and monopolar electrosurgery techniques), isotonic saline may be used during the procedure. Saline is the preferred medium for irrigation because it has the same concentration as the body""s fluids and, therefore, is not absorbed into the body as much as other fluids.
In another aspect of the invention, a method comprises positioning one or more resection electrode(s) adjacent the target tissue, and applying high frequency voltage between the resection electrode(s) and one or more return electrode(s) to resect a tissue fragment away from the tissue structure. High frequency voltage is then applied between one or more ablation electrode(s) and one or more return electrode(s) to ablate the tissue fragment in situ. The ablation electrode(s) may be the same electrodes as the resection electrode(s), or they may be different electrodes spaced from the resection electrode(s). Removing the resected tissue fragments improves the surgeon""s visibility of the target site, and eliminates the potential of this tissue from remaining in the body after the surgical procedure.
Alternatively, the loop electrode(s) may be used to ablate (i.e., volumetrically remove) tissue directly at the target site using the mechanisms described above. Applicant has found that the loop electrode(s) have a larger surface area exposed to electrically conductive fluid than the active electrode terminals described above. Therefore, the loop electrode(s) typically provide a stronger plasma layer, which leads to faster tissue ablation rates for the same applied voltage levels. In addition, the loop electrode configuration provides a relative smooth, uniform cutting effect across the tissue.
In a specific configuration, an electrosurgical probe according to the invention comprises a shaft having an electrically insulating support at or near the distal end of the shaft. The instrument further includes one or more loop electrode(s) extending from the insulating support for resection or ablation of tissue, and one or more electrode terminal(s) for ablation of tissue fragments that have been resected by the loop electrode(s.) The electrode terminal(s) may comprise an array of electrode terminals or a single electrode at the distal end of the electrosurgical probe. In a specific embodiment, one or more return electrode(s) are positioned in contact with electrically conducting fluid to provide a current flow path from the electrode terminal(s), through the electrically conducting fluid, to the return electrode(s).
In yet another aspect of the invention, a method comprises positioning one or more active electrode(s) at the target site within a patient""s body and applying a suction force to a tissue structure to draw the tissue structure to the active electrode(s). High frequency voltage is then applied between the active electrode(s) and one or more return electrode(s) to ablate the tissue structure. Typically, the tissue structure comprises a flexible or elastic connective tissue, such as synovial tissue. This type of tissue is typically difficult to remove with conventional mechanical and electrosurgery techniques because the tissue moves away from the instrument. The present invention, by contrast, draws the elastic tissue towards the active electrodes, and then ablates this tissue with the mechanisms described above